The present invention relates to private wireless networks for communication between a number of wireless terminals, both public and private, which are free to join and leave the network at any time. The network may be configured so that all the wireless terminals communicate through a base station, or so that the devices communicate directly with one another.
Wireless networks are intended to offer flexible and cost-effective alternatives to wired networks, for example as Local Area Networks (LANs). An advantage of wireless over fixed networks is the ease with which new networks can be created and with which new devices, known as wireless terminals, can be added to the network. Some wireless network standards exist, for example IEEE 802.11 in the USA and HIPERLAN in Europe, whilst others are under development, for example Wireless Asynchronous Transfer Mode (WATM). Such standards define the format of a transmission frame, within which control and data transfer functions can take place. The format and length of transmission frames may be fixed or dynamically variable.
Known wireless networks, for instance as disclosed in U.S. Pat. No. 5,274,841, typically operate in one of two different configurations:
1. A base station orientated configuration in which wireless terminals can only communicate with each other with the support of a base station, which is responsible for all wireless terminals within a certain radio coverage area. The base station itself may be connected to further wired networks for communications beyond the radio coverage area. The base station may be a separate unit, or it may be a wireless terminal with additional functionality.
2. A peer to peer configuration in which wireless terminals communicate directly with one another. One of the wireless terminals is typically chosen dynamically to perform the control function.
The first configuration is generally considered to be most suitable for networks with a relatively fixed structure, while the second is considered most suitable for the generation of dynamic networks, such as for document exchange at a meeting.
In order for a wireless network to realise the advantage of flexibility, the procedure for wireless terminals joining and leaving the network should be as simple as possible. The act of a wireless terminal joining a network is known as association and needs to be scheduled within the data transmission format defined for the wireless network. Examples of known techniques for association include dynamic framelength slotted ALOHA, described in GB-B-2 069 799, carrier sense multiple access and address based tree resolution algorithms.
A problem with known wireless networks is that security can be compromised if the network is open to any wireless terminal, but flexibility is sacrificed if access is limited to a known set of wireless terminals.